A known problem with vacuum pumps consists in that they cannot function at high pressures for a long period of time because of the risk of thermal overload. If a vacuum pump is started at a high pressure, it will work for an extensive amount of time at maximum capacity, which generates heat and might cause a malfunction.
Another risk associated with a vacuum pump starting at a high pressure, is the elevated risk of having oil emissions at the discharge channel of the vacuum pump.
Yet another aspect that needs to be taken into account is the risk of encountering significant pressure fluctuations in a relatively short time interval at the inlet of the vacuum pump which can cause current fluctuations in the motor driving said vacuum pump, and associated unwanted effects such as the tripping of the motor.
Because of these risks, different methods for protecting the vacuum pumps have been introduced. Some vacuum pumps split the process of achieving the required pressure value in intermediate stages and use multiple pumps, others suggest a reduction of the pressure at the inlet of the vacuum pump before starting it. One significant drawback of both proposed methods is the increase in design complexity. Because the design becomes more complex, the dimensions of the overall system, the manufacturing and maintenance costs increase considerably. Another significant drawback of these vacuum pumps consists in that an extensive waiting time interval is required until the desired pressure is achieved, because either multiple stages are required, or an initial waiting time interval for lowering the pressure at the inlet of the vacuum pump is needed. Yet another drawback the these vacuum pumps is the fact that they do not solve the problems associated with sudden pressure fluctuations at the inlet of the vacuum pump. Because of this, the reliability and responsiveness of such vacuum pumps is limited.
Other methods include the use of a system of valves for regulating the pressure on the vacuum line. One example can be found in U.S. Pat. No. 4,273,154 wherein a system using two valves, a main valve and an auxiliary valve, is being introduced. The system makes use of a coil spring to generate the necessary force in order to control the position of the auxiliary valve. The vacuum line is in fluid communication with a control chamber and with a first auxiliary chamber delimited by the auxiliary valve and the spring. When the pressure in the vacuum line drops, the pressure within the first auxiliary chamber also drops. When the pressure is sufficiently low, the auxiliary valve lifts and outside air from a second auxiliary chamber enters through channels inside the vacuum line. This results in that the pressure inside the control chamber increases, causing the main valve to open and allowing a flow of outside air to enter in the vacuum line, causing the pressure therein to increase.
Due to the complex assembly of communicating channels, the module introduced by U.S. Pat. No. 4,273,154 is not sufficiently responsive to achieve a relatively constant pressure on the vacuum line. Because of such complex assembly and because the system also uses multiple membranes, the risk of malfunctions increases considerably, making the system proposed by U.S. Pat. No. 4,273,154 not only extremely complex to manufacture but also extremely costly when it comes to assembly and maintenance.
If dealing with oil injected vacuum pumps, another important aspect that needs to be taken into account is the need to maintain the oil flow within the system. For this purpose, known vacuum pumps use an oil pump to maintain the circulation of oil between the vacuum element and an oil separator. If such an oil pump would not be present or would not function properly, the pressure difference between different areas of the vacuum pump would not be sufficiently high to keep the oil circulating therein and, as a result, dangerously high temperatures and low efficiency of the vacuum process would be encountered. One of the drawbacks of known systems when using such a structure for a vacuum pump is the significant increase in manufacturing costs of the overall system and the significant increase of complexity of the overall circuit.
Yet another important aspect that needs to be taken into account when using oil injected vacuum pumps is the high risk of oil emissions within the process chamber once the vacuum element is being shut off, which means a high risk of oil contamination of the end product. An existing solution for this problem is the use of a series of valves connected on the inlet channel of the vacuum pump that allow a controlled flow of gas for a predetermined time interval after the vacuum element is being shut off. Such a solution is extremely costly and increases the complexity of the overall system.
Taking the above drawbacks into consideration, it is an object of the present invention to provide a valve regulating the pressure at the inlet of the vacuum element such that the vacuum pump can function through the entire range of pressures without being damaged. The valve according to the present invention further aims to achieve a user friendly solution for regulating the pressure at the inlet of the vacuum element.